Friday, August 15, 2014

Get used to hearing about these semi-corpulent beastsbecause between now and the end of September a lot of news is going to hit surrounding this format.

These are not fat bikes, but some call them "semi-fat bikes". These bikes will be primarily based on two wheel sizes, but the old 26/559ISO will also have "plus sized" rubber news as well. So......just what is this and WHY?!!

Typically mountain bike tires for general purpose riding go between 2 inches and 2.5 inches in width. I think it is safe to say that is the case with most 26 inch tires and almost all 27.5 and 29 inch sized tires. (Of course, there are exceptions.)

26" is ISO 559

27.5/650B is ISO 584

29" is ISO 622

That above means that these tires listed as inch sizes or in the case of 650B, a french derivative sizing scheme, all fit on their respective ISO rim bead seat sizes. Taking into account the width of most tires for off road riding, you get what you have come to know as "normal". The plus sized scheme doesn't change what tires fit on ISO bead seat diameters, but it does increase the width and volume of the tires that fit on those specific rims. Plus = more. More width, more volume, more traction, and more fun. It just doesn't get so big as to become "fat bike" sized, which is generally agreed upon starting at 3.8" in width for a tire.

29+: A bigger, wider 29"er tire that isn't 29" at all!

Back Story: You can mostly blame "plus" sized tires on Surly Bikes. They popped out this Krampus bicycle with the 29+ sized tires a couple of years back at the trade shows. It basically is a hard tail tweaked for trail duty shod with three inch wide tires that fit on a ISO 622 rims, which are wider themselves to better support the tire. However big these rims seem to be, they are the same diameter as a road racing bike's rims. What makes them seem so cartoonish is the volume and width of the tire that fits on it in this case. The 29+ is actually not a 29"er tire at all. The actual outer diameter is closer to 31" overall.

This is why a 29+ tire on a 29"er wheel won't fit on a 29"er, because it actually a 31"er! (Well- 30.7", to be exact) The width also precludes usage on almost all 29"ers out there. So, you need a special frame. There are some out available, but they are few and far between, besides the ubiquitous Krampus, of course.

But what if you could put a "plus sized" tire on a 29"er bike without modifying anything? Then the only thing you'd need to buy would be the wheels. Well, theoretically speaking. That is the premise behind the "B+" wheels. These wheels would be your 27.5"/650B rim, (584 ISO), shod with a 2.8" tire. On a wider rim, you would get a similar contact patch that a 29+ tire would have yet it would, (again- theoretically), fit your current 29"er. Cheaper to buy into, and it would totally transform your 29"er. Plus, the overall diameter, (said to be just shy of 29 inches), would work for a wider range of human beings.

It'll be real interesting to see what comes out this Late Summer/Early Fall, and just how manufacturers will interpret this idea.

TIMP Update:

We've got a couple of scheduled rides to go yet on the Trans Iowa Masters Program. The one that is coming up today is Al Brunner's TIMP ITT attempt. Follow Al's SPOT tracker by clicking the hyperlink back there.

Mike Johnson is the only other scheduled ride and that is also an ITT, (Individual Time Trial), ride. After Mike's attempt, I think that'll be it for the TIMP. I haven't gotten any word or even a hint about any last minute attempts. Of course. after August 31st, it's all over with. I'll likely give an overview on the TIMP after August passes, so look for that coming soon.